Transmission system



June 15, 1937. R. D. FRAcAssl 2,083,645

I TRANSMISSION SYSTEM Filed Oct. 12, 19:54 2 Sheets-Sheet 1 l INVENTORAvAvA'A i J me w ATTORNEY June 15, 1937. R. D. FRACASSI I 2,033,645

TRANSMISSION SYSTEM Filed Oct. 12, 1934 2 Sheets-Sheet 2 INVENTORATTORNEY Patented June 15, 1937 UNITED STATES PATENT OFFICE TRANSMISSIONSYSTEM Renato Dario Fracassi, Jackson Heights, N. Y., assignor toAmerican Telephone and Telegraph Company, a corporation of New York Thisinvention relates to transmission lines, and more particularly totransmission lines having repeaters included therein.

In transmission lines having included therein 5 repeaters of the type,for example, comprising two one-way line sections with vacuum tubeamplifiers therein for transmission in opposite directions and havingthese line sections interconnected through hybrid coils, there may be atend- 10 ency for the repeater to sing. This might be due to acirculation of energy taking place from one line section through onehybrid coil to the other line section and then through the other hybridcoil back to the first line section. Under certain 5 conditions thiscirculation of energy will cause singing which will interfere withtransmission as is well known in the art.

The arrangements of the present invention are such that when no speechcurrents are present 20 on the line a loss is introduced in thetransmission path of the repeater. This will tend to prevent singing.When speech currents are present on the line, the arrangements of theinvention remove the loss in the direction of transmission and alsosuppress transmission in the opposite direction so as to prevent theoccurrence of singing and to prevent echo currents from returning to thetalker. Thus the arrangements of the invention will improve the singingmargin when no speech currents are present. When speech currents arepresent the arrangement W111 permlt the introduction of additional gainin the direction of transmission and at the same time its echosuppressor action will prevent singing from occurring and echo currentsfrom returning/to the talker. Other objects and features of theinvention will appear more fully from the detailed description thereofhereinafter given.

The invention may be more fully understood 40 from the followingdescription together with the accompanying drawings in the Figures 1, 2,3, and 4 of which the invention is illustrated. Fig. 1 is a circuitdiagram showing a preferred embodiment of the invention as applied at arepeater 45 station. Fig. 2 is a modification of Fig. 1. Fig. 3 is acircuit diagram showing the arrangements of the invention as applied toa multi-way connection, and Fig. 4 is a circuit diagram showing afurther modification of the invention. The ar- 50 rangements shown byFigs. 1, 2, and 4 may also be used with multi-way connections. Similarreference characters have been used to denote like parts in all of thefigures.

In Fig. 1, the invention is shown as applied to a repeaterinterconnecting the line sections L1 and L2. The repeater comprises theusual hybrid coils I and 2 and balancing networks'Ni and N2. Twocircuits 3 and 4 are provided, each having amplifying devices such as 5and 6. Associated with the hybrid coil I is a circuit 7 having in- 5eluded therein an impedance 9. This serves to introduce a loss in thetransmission of currents through the hybrid coil I. Similarly, a circuit8 is associated with the hybrid coil 2 and includes an impedance I0.This serves to introduce a loss 10 in the transmission of currentsthrough the hybrid coil 2. When speech currents are not transmitted overeither of the line sections L1 or L2, these losses are inserted in thesystem and act to prevent singing due to a circulation of energy throughthe repeater.

Associated with the circuit v3 is a detector device II and associatedwith the circuit 4 is a detector device I2. When speech currents aretransmitted over one of the line sections as, for example, from the lineL2, these speech currents will actuate the detector device I I and causethe relay I3 to be operated. This will open the circuit 1 and remove theloss introduced thereby from the system. The operation of the relay I3will also close a circuit I 5 which will short-circuit the circuit 4 inthe manner of the wellknown echo suppressor. In like manner, when speechcurrents come in over the line L1, the detector device" will be operatedand, in turn, will operate the relay I4. The operation of the relay I4will open the circuit 8 and remove the loss introduced thereby from thesystem. The operation of relay I4 will close the circuit I6 andshort-circuit the circuit 3 in the manner of the well known echosuppressor. With this arrangement, it will be seen that when no speechcurrents are being transmitted, a loss will be introduced in the systemand will tend to prevent singing from currents other than speechcurrents. However, when speech currents are transmitted over the system,the loss is removed, or, in other words, additional gain is introducedin the repeater circuit without impairing the singing margin, sincesinging cannot occur with one circuit disabled by the short circuit. P lf- Fig. 2 is a modification of the arrangements 01' Fig. 1. Thearrangements of Fig. 2 are substantially similar to those of Fig. 1except that two additional relays such as I8 and 2| are provided. InFig. 2, when speech currents come in over the line L2, the detectordevice II is actuated and operates relay It. This will open the circuitI and remove the loss introduced thereby from the system. The operationof the detector II will also, through the agency of circuit 285, actuatethe relay 2| which, in turn, will close a short circuit 22 over thecircuit i in the manner of the well known echo suppressor. In likemanner, speech currents coming in over the line L1 will actuate thedetector device l2 which will operate the relay M which, in turn, willopen the circuit 8 and remove the loss introduced thereby from thesystem. The operation of detector i2 will, through circuit ll, operatethe relay It and close a short circuit l9 across circuit 3 in the mannerof the well known echo suppressor.

It will be seen that in this arrangement as in the previous arrangement,a loss is introduced in 5 the system when speech currents are not on theline and this loss is removed when the speech currents are transmittedthereover. At the same time the line in the direction opposite to thatof speech transmission is disabled.

Fig. 3 shows an arrangement of the invention which may be used whenmulti-wave connections are established as, for example, between the lineL4 and other lines, such as L6 and L3. The line L4 is connected to theline L3 through repeater apparatus A shown within the dotted lines. Thisrepeater apparatus comprises the usual hybrid coils and 26 and thebalancing networks Na and N4. It comprises two circuits 2'! and whichhave included therein amplifier devices 30 such as 29 and 35. Associatedwith the hybrid coil 25 will be a circuit having included there in animpedance 35. This will serve to intro duce a loss in transmission ofcurrents through the hybrid coil 25. This loss will tend to preventsinging which would be caused by currents other than voice currents.When the voice currents come in from line L4, the detector device 3|will cause the relay 33 to be operated. This will open the circuit 35and remove the loss introduced by the impedance 38. When voice currentscome in over the line La, the detector device 32 will actuate the relay34 and cause a short circuit across the circuit 2'? in the manner of thewell known echo suppressor. The line L3 would be associated with acommon line Ls. Bridged across this line might be other lines such as L5and L7. These lines would be connected to apparatus similar to A,originally referred to and enclosed in the dotted lines. This apparatuswould be connected to other lines such as L6 and LB.

With such an arrangement loss is introduced in only one direction ofeach repeater, said loss being removed when speech currents aretransmitted in that direction. When speech currents are transmitted inthe other direction echo suppressor action takes place which disablesthe side of the repeater transmitting in the direction opposite to thatof speech transmission. This arrangement is particularly adapted for useon circuit arrangements where two or more such devices can be used atspecified points, such as the separate points along a transmission lineor in a multi-way connection as shown in Fig. 3. When properly used oneof the arrangements removes loss in the direction of transmission whilethe remaining devices act to suppress echoes. The action of eacharrangement is reversed when the direction of transmission through it isreversed.

Referring to Fig. 3 when transmission is from L4 to L3 and thence to L5,L6, L7, La, etc., the loss is removed from the path through the hybridcoil 25 but remains in all other paths associated with La, La, etc. Echosuppressor action takes place in the apparatus designated A associatedwith L6, L3, etc.

- In multi-repeatered two-wire circuits or in multi-way interconnectingcircuits, such as represented by Fig. 3, a plurality of singing pathsexists as enumerated below.

First, there are so-called local paths, that is, involving only onerepeater. Referring to Fig. 3 such a path begins at L4, thence throughthe amplifier element 29, thence tothe hybrid coil 25,

thence to the amplifier element 38 by means of the transmission pathbrought about by the unbalance between 1.13 and its associated networkN3 and finally back to L4 through hybrid coil 26. In the passive state(no speech currents) the loss introduced by the impedance 85 decreasesthe tendency to sing around this local path.

In addition to the above there are so-called combined paths, that is,paths involving a plurality of repeaters. path involving two repeatersbegins at L4, thence through the amplifier 29 t the hybrid coil 25,thence to L3, thence through L9 to L5, thence through the amplifier tothe hybrid coil associated with L6, thence through the unbalance betweenLa and its associated network Ne, thence through the amplifiertransmitting back toward L5, thence to the hybrid coil associated withL5, then to L5, thence to L9, thence to L3, thence to the hybrid coil25, thence to. amplifier 3Q, thence through the hybrid coil 26 to L4.

In the passive state (no speech currents) each path involves a number oflosses introduced corresponding to that introduced by the impedance 36,the number of such losses corresponding to the number of repeatersinvolved in the path.

In a multi-way connection as illustrated by Fig. 3 in the active state(speech currents existing) only one of the above losses is removed, saidremoved loss being that associated with the repeater connected to thetalkers line. The removal of this loss impairs the singing margin aroundthe local path as such but singing is assumed to be prevented by thebalance between L3 and Na and also between L4 and N4. All other pathsare short-circuited by the echo suppressor action taking place in thedevices associated with the other repeaters.

In the arrangement shown in Fig. 4 there is illustrated a two-wire linesection L1 and a fourwire line section composed of sections L2 and L2".These line sections are interconnected by repeaters 5 and 6. Repeater 6is connected to the line section L1 by means of the hybrid coil andtransformer 59. The repeater 6 is connected to the line section L2 bymeans of the transformer-5i. The repeater 5 is connected to line sectionb" by means of transformer 52 and to the line section L1 by means oftransformer 53 and the hybrid coil I.

When speech currents are transmitted from the line section L1 over thehybrid coil I they act upon the detector l2 and the detected currentsoperate the relays M and I8. The relay M will open the circuit of itscontact and remove the loss introduced by the coil which is connected inseries with that contact. At the same time the operation of relay !8will place a short-circuit about the primary winding of the transformer52 for the purpose of echo suppressor action. The removal of the loss bythe action of relay [4 will cause an increase in the level of energytransmitted through the repeater 6 and over the line section L2.

When speech currents are received from the For illustration one suchline section L2" they will reach the detector II, which will act uponthese currents, and the detected currents will operate relays l3 and 2|.The relay I3 will open the contact associated therewith and hence removethe loss provided by the coil which is coupled to the primary winding ofthe transformer 53. The operation of the relay 2| will place ashort-circuit across the line connected to the primary winding of thetransformer 50 for the purpose of echo suppressor action. The removal ofthe loss by the operation of relay I3 will cause an increase in thelevel of energy transmitted through repeater 5 and through thetransformer 53 and the hybrid coil l to the line section L1.

Thus it is evident that the use of the arrange ments shown in any oftheir forms tends to improve greatly the over-all singing margin sinceit adds attenuation or completely removes the so-called combined singingpaths, leaving at the most a single open path wherein sufiicient singingmargin may be easily maintained.

While the invention has been disclosed as embodied in certain specificarrangements which are deemed desirable, it is understood that it iscapable of embodiment in many and other widely varied forms withoutdeparting from the spirit of the invention as defined by the appendedclaims.

What is claimed is:

1. In a two-way communication system, the combination of a two-waytelephone repeater having two hybrid coil networks adapted to transmitsignaling currents in the two directions over different paths, meansresponsive to signaling currents in one path to remove loss from saidpath and to insert loss in the other path, one of said losses beinginductively coupled to its associated hybrid coil network, said meansconsisting of an amplifier-detector, an impedance, shortcircuiting meansand a relay, said relay removing said impedance from across one of thewindings of the hybrid coil network in the path transmitting signalingcurrents and connecting the short-circuiting means across the bridgepoints of the same hybrid coil network.

2. A transmission line comprising two line sections interconnected by arepeatered transmission system, said repeatered transmission systemcomprising two one-way circuits having amplifiers therein and two hybridcoils for conmeeting said one-way circuits to said line sections, a pairof resistances each connected across one of the windings of said hybridcoils and inductively coupled to the respective one-way circuits, andmeans responsive. to the transmission of currents of a certain type overthe corresponding one-way circuit for opening the circuit of thecorresponding resistance and for shunting the circuit of the otherone-way circuit.

3. In a two-way communication system, the combination of a two-waytelephone repeater having two hybrid coil networks adapted to transmitsignaling currents in two directions over different paths, meansresponsive to signaling currents in one path to remove loss from saidpath and to insert loss in the other path, said means consisting of anamplifier-detector, an impedance coupled to each hybrid coil network,shortcircuiting means, and a relay, said relay removing one of saidimpedances from across one of the windings of its corresponding hybridcoil network in the path transmitting signaling currents and connectingthe short-circuiting means across i the bridge points of the same hybridcoil net- Work.

RENA'IO DARIO FRACASSI.

